1. Field of the Invention
The present invention relates to data storage devices for performing one or both data record and data reproduction by moving a storage medium and a head relative to each other. The present invention can apply, for example, to magnetic disk devices including a hard disk drive as a storage medium.
2. Description of the Related Art
Magnetic disk devices have recently been used in various types of equipment such as car navigation systems and portable music players with a neck strap, in addition to external storage devices for computers. Along with this diversification, environment to be expected for the use expand to include harsh environment where temperature or humidity fluctuates substantially and where a major impact force is exerted in unspecified directions. Even when usage patterns of magnetic disk devices are diversified as described above, the importance of preventing data loss remains unchanged.
Magnetic disk devices including hard disk drives are configured to have a closed shape for preventing dust from adhering to disks. In practice, however, the inside is connected to the outside air through a filter. The reason for the closed shape is that a head is placed only an extremely short distance of approximately 10 nm above a spinning disk for record and reproduction (for writing and reading). Such a closed structure is called a disk enclosure, i.e., a DE for short. The disk enclosure houses a head gimbal assembly (HGA), a voice coil motor (VCM), a head amplifier (HDA) and a spindle motor (SPM) together with a disk. Some disk enclosures house plural disks for the purpose of increasing storage capacity.
The effect of mechanical shock on a magnetic disk device depends on the direction of an impact force. In general, the effect of shock in the circumferential direction of a disk, i.e., in the direction of relative movement between the disk and a head is relatively small. The shock in the disk diameter direction, i.e., in the seek direction causes off-track that the head does not follow predetermined tracks, resulting in an access error. A head slider accidentally touches the disk due to the shock in the rotation axis direction of the disk. The accidental touch is called a crash due to which the disk surface is partially cut and dust scatter. The scattered dust incurs further crash. The resistance to external forces of a typical head gimbal assembly is relatively low with respect to the force in the direction along which the head is pulled from the disk. However, it is relatively high with respect to the force in the direction along which the head is pushed toward the disk. In the case of a double-sided recordable disk, a force for pulling a head from one surface of a disk works to move the head away from the other surface of the disk.
Japanese unexamined patent publication No. 6-259861 is a related art document concerning data integrity toward mechanical shock. The publication discloses that, in a system including a plurality of magnetic disk devices and having a configuration capable of mirroring, magnetic disk devices serving as masters in mirroring and magnetic disk devices serving as shadows in mirroring are arranged in a manner to make their disk surfaces different between these devices. In the system configuration disclosed in the publication, when shock in a certain direction is applied to the system, one of the master magnetic device and the shadow magnetic device is less affected than the other. In other words, the probability is low that both the master magnetic devices and the shadow magnetic devices become inaccessible due to shock, compared to the configuration in which all magnetic disk devices are arranged in the same orientation.
Japanese unexamined patent publication No. 11-45530 describes a magnetic disk device including acceleration sensors. This magnetic disk device monitors external forces using the acceleration sensors and moves a slider away from a record/reproduction area when a predetermined external force is applied.
Data storage devices with plural disk enclosures have been expected to be used as relatively large equipment used with being fixedly installed like servers or large-capacity storages. The data storage devices of the type have not been expected to be used as small equipment used under the situation where unspecified vibration or shock is often applied, like in-vehicle equipment or portable players. For this reason, when the conventional data storage devices are used under the environment where vibration or shock is often applied, serious malfunction causing data loss may occur or the situation where access is interrupted due to retraction control may continue for a long period of time.